[Insight-developers] Bug in ImageFunction causing incorrect results from ResampleImageFilter

[Stefan Klein]

Hi Dan,

I'm not sure, but: it seems that with the current implementation the 
valid range is:

[0, N-1]

instead of [0,N-1) as you said.

(if index==m_EndContinuousIndex the method returns true).

In my opinion, the current implementation is right. For example, I see 
no meaningful default implementation for a linear interpolator at 
indices > N-1. (unless some boundary condition has been set).

Moreover, related to the discussion on the voxel centre (IndexToPoint 
conversion): wouldn't it be more logical to define the valid region as 
going from -0.5 to N-0.5?
(but that would cause troubles again for some interpolators, so i would 
vote to keep it like it is right now)

Kind regards!
Stefan


Blezek, Daniel J., Ph.D. wrote:
> I have some fairly thick CT slices (5mm) that I would like to resample
> to be isotropic.  A straightforward use of ResampleImageFilter leaves 4
> blank slices in the output volume.  I've tracked this down to a bug(?)
> in ImageFunction.  This code is incorrect IMHO:
> 
>   virtual bool IsInsideBuffer( const ContinuousIndexType & index ) const
>     { 
>       for ( unsigned int j = 0; j < ImageDimension; j++ )
>         {
>         if ( index[j] < m_StartContinuousIndex[j] ) { return false; };
>         if ( index[j] > m_EndContinuousIndex[j] ) { return false; };
>         }
>       return true;
>     }
> 
> (Dealing with Z in 3D) This code assumes the last slice has zero
> thickness.  For N slices, the range where IsInsideBuffer returns true is
> [0, N-1).  This is incorrect, the correct result should be [0, N).  [0,
> N) gives the last slice it's proper thickness.  The windowed Sinc
> interpolator properly handles the last slice, i.e. [N-1, N), but I have
> not checked others.  A proper implementation would look like this (note
> the vcl_floor calls):
> 
>           if ( vcl_floor(index[j]) < m_StartContinuousIndex[j] ) {
> return false; };
>           if ( vcl_floor(index[j]) > m_EndContinuousIndex[j] ) { return
> false; };
> 
> 
> I've run all the tests on a fresh check out with the above change.  As
> may be expected, almost all of the registration tests fail, while most
> of the resample tests pass.  Surprisingly,
> ResampleVolumesToBeIsotropicTest passed...
> 
> Any comments on this bug?  Should the tests be made to accommodate the
> change, or should I override the method in a custom interpolator?
> 
> Regards,
> -dan
> 
> 
> 
> Daniel Blezek, PhD
> Medical Imaging Informatics Innovation Center
> Enterprise Imaging Systems Unit
> 
> P 127 or (77) 8 8886
> T 507 538 8886
> E blezek.daniel at mayo.edu
> 
> Mayo Clinic
> 200 First St. S.W.
> Harwick SL-44
> Rochester, MN 55905
> mayoclinic.org
> 
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